It is known to manufacture objects of superconductive materials in the form of an oxide by isostatic pressing of a body preformed from a powdered material at a temperature necessary for sintering of the preformed body. The powder material comprises an oxide of the metals contained in the superconductive material. The starting powder material used often constitutes another, nonsuperconductive modification of the same oxide as the superconductive material consists of. The superconductive material is then formed of the powder material during the heat treatment to which the powder material is subjected when the object is manufactured. It is also possible to use a powder material in the form of the superconductive modification as starting material.
When the preformed body is subjected to the isostatic pressing at the sintering temperature according to the known method in order to give a desired dense, sintered product it is enclosed in a casing which, during the pressing, can prevent the pressure medium used, e.g., an inert or reducing gas, from penetrating into the powder body. It has been proved that such a method of manufacture is associated with problems which, at least to a great extent, can be ascribed to the great propensity of the powder material to give off oxygen at the temperature required for the pressing. This causes many materials which could be used for the casing to become oxidized, while the material in the preformed body is depleted of oxygen. Such a process may cause defects on the materials in the casing which deteriorate their ability to function as a gas-tight casing. Many other materials for the casing which withstand oxidation allow oxygen to diffuse through the casing, which also results in depletion of the preformed body with respect to oxygen. Such a depletion requires an after-treatment of the pressed and sintered object with oxygen to restore its original oxygen content. In that connection it may be difficult to achieve an end product with a desired crystalline structure which is uniform and free from phases without superconductivity. Such phases of an irreversible kind may be formed during the treatment. Because of the existing problems, it is difficult, with the technique used so far, to manufacture objects with the desired properties with an acceptable reproducibility.